Method of detecting sound using a micro-electro-mechanical system optical microphone

ABSTRACT

A micro-electro-mechanical system (MEMS) optical sensor, method of detecting sound using the MEMS optical sensor and method of manufacturing. The MEMS optical sensor including a substrate having a base portion and a vertically extending support portion. The sensor further including a top plate having a compliant membrane configured to vibrate in response to acoustic waves, the top plate connected to the support portion and having a reflective surface. The sensor also includes a back plate connected to the support portion, the back plate having a grating portion positioned below the reflective surface portion and a base plate connected to the support portion at a position below the back plate. A light emitter, a light detector and circuitry operable to tilt the top plate and the back plate with respect to the base plate so as to direct the reflected laser light toward the light detector are further provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a divisional of co-pending U.S. application Ser. No.14/330,723 filed on Jul. 14, 2014 which claims the benefit of theearlier filing date of U.S. Provisional Patent Application No.61/991,067, filed May 9, 2014 and incorporated herein by reference.

FIELD

An embodiment of the invention is directed to a micro-electro-mechanicalsystem (MEMS) device having a tilted plate, more specifically, a MEMSoptical microphone having a tilted compliant membrane and back plate.Other embodiments are also described and claimed.

BACKGROUND

MEMS devices generally range in size from about 20 micrometers to about1 millimeter and are made up of a number of even smaller componentswhich can be formed in layers on a substrate using various MEMSprocessing techniques (e.g. deposition processes, patterning,lithography, etching, etc.). MEMS devices can be processed for manydifferent applications, for example, they may be sensors or actuators.One such type of MEMS sensor is a laser microphone. A MEMS laser, oroptical, microphone refers to a microphone which uses a laser beam todetect sound vibrations of an associated diaphragm. The microphone mayinclude two essentially flat, horizontally arranged, surfaces. One ofthe surfaces may be a diaphragm, which can vibrate in response to soundwaves, and the other surface may be a substantially stiff structurehaving a grating. A light emitter and a light detector may be associatedwith a substrate positioned below the flat surfaces. The light emittermay be a laser (e.g. a vertical cavity surface emitting laser (VCSEL))configured to direct a light beam toward a reflective portion of thediaphragm. The light beam is diffracted by the grating and reflected offof the reflective portion back to the light detector. The light detectordetects the interference pattern created by the diffracted light raysand converts the light into an electrical signal, which corresponds toan acoustic vibration of the diaphragm, which in turn provides anindication of sound.

SUMMARY

An embodiment of the invention is directed to a MEMS sensor such as avery high SNR (signal-to-noise ratio) laser (or optical) MEMS microphonehaving one or more layers, plates or membranes which can be tilted tomodify an alignment between a light source (which is stationary) and areflective layer (e.g. a diaphragm having a reflective portion). Forproper operation of an optical microphone, the light beam from the lightsource should be properly aligned with a reflective portion of thediaphragm. Proper alignment, however, can be difficult in MEMS typestructures in which it is not feasible to mass manufacture tiltedsurfaces and layers. The MEMS sensor can be formed by MEMS processingtechniques suitable for forming one or more plates (e.g. electrodes)which can be tilted.

An embodiment of the invention solves the alignment problem in anoptical microphone by allowing for the manufacture of a MEMS structure,for example, an optical MEMS microphone, having a compliant membrane(e.g. diaphragm) with a reflective surface and a back plate having agrating, both of which can be tilted, with respect to a light source, byapplying a voltage. Representatively, the compliant membrane may beformed over a substrate and may have a reflective surface portion. Thecompliant membrane may have a first end movably connected to avertically extending portion of the substrate, and a second, free end.The back plate may be positioned below, and substantially parallel to,the compliant membrane and may include a grating portion. The back platemay have a first end movably connected to the vertically extendingportion of the substrate and a second, free end. A base plate extendingsubstantially horizontally from a portion of the vertically extendingportion of the substrate and spaced a distance below the free ends ofthe compliant membrane and back plate is further provided. A lightsource (e.g. a vertical-cavity surface-emitting laser (VCSEL)),positioned on the substrate, below the compliant membrane and backplate, is directed toward the grating of the back plate and reflectivesurface portion of the compliant membrane. A light detector may furtherbe positioned on the substrate to detect a pattern of light reflectedoff of the compliant membrane and back plate grating (i.e. aninterference pattern). The pattern represents a displacement of thecompliant membrane caused by sound pressure waves, and therefore can beused to provide an indication of sound. In this aspect, the MEMS deviceuses a diffraction based optical interferometer method to provide anindication of sound. Circuitry may further be connected to the compliantmembrane, the back plate, the base plate, the light emitter and/or thelight detector.

During operation, application of a voltage by the circuitry causeselectrostatic forces between the compliant membrane, the back plate andthe base plate to tilt the compliant membrane and the back plate towardthe base plate (which is stationary). In one embodiment, in the restingposition (i.e. no voltage) the compliant membrane, the back plate andthe base plate are substantially parallel to one another, in what may bedescribed as a “horizontal” position. In the active position (i.e.voltage is applied), the free end of the back plate moves toward thebase plate to tilt the back plate and set the tilt angle and the freeend of the compliant membrane moves toward the back plate to tilt thecompliant membrane. The tilt angle may be an acute angle, for example,less than 4 degrees, or for example, 3 degrees or less. In someembodiments, the tilt angle is a predetermined, set, angle such that theback plate and compliant membrane are either tilted at the set tiltangle or they are not tilted and in the horizontal position. In otherembodiments, the tilt angle can vary depending upon the voltage applied.In other words, the application of a smaller voltage will result in adifferent tilt angle (e.g. smaller tilt angle) then when a largervoltage is applied (e.g. larger tilt angle). Spacers or posts mayfurther be provided between the compliant membrane, the back plate andthe support arm to avoid stiction and define a controlled minimal stressregion of operation for the compliant membrane.

A process for manufacturing a MEMS optical microphone may includeproviding a substrate and forming a base plate layer over the substrate.A back plate layer may be formed over the base plate layer and acompliant membrane layer may be formed over the back plate layer. Alight emitter and a light detector may be connected to the substrate. Inaddition, directional circuitry may be connected to the base platelayer, the back plate layer and the compliant membrane layer. Thecircuitry is operable to cause the back plate layer and the compliantmembrane layer to tilt with respect to the base plate layer when avoltage is applied so as to modify an alignment between a reflectiveportion of the compliant membrane layer and the light source and directthe reflected light toward the light detector. In some embodiments,prior to forming the base plate layer, the back plate layer and thecompliant membrane layer, a sacrificial layer is formed between eachlayer to define a gap between each of the layers, and then subsequentlyremoved. Each of the layers may be formed using MEMS processingtechniques.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the Detailed Description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and they mean at least one.

FIG. 1A illustrates a cross-sectional side view of one embodiment of aMEMS device.

FIG. 1B illustrates the MEMS device of FIG. 1A in a tiltedconfiguration.

FIG. 2A illustrates a cross-sectional side view of one embodiment of aMEMS optical microphone.

FIG. 2B illustrates the optical microphone of FIG. 2A in a tiltedconfiguration.

FIG. 3 illustrates a top view of the compliant membrane of the opticalmicrophone of FIG. 2A.

FIG. 4 illustrates a bottom view of the compliant membrane of FIG. 3.

FIG. 5 illustrates a top view of a back plate of the optical microphoneof FIG. 2A.

FIG. 6 illustrates a bottom view of the back plate of FIG. 5.

FIG. 7A illustrates one embodiment of a processing step for fabricatingthe optical microphone of FIG. 2A.

FIG. 7B illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7C illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7D illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7E illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7F illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7G illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7H illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7I illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 7J illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A.

FIG. 8 illustrates one embodiment of a simplified schematic view of oneembodiment of an electronic device in which the optical microphone maybe implemented.

FIG. 9 illustrates a block diagram of some of the constituent componentsof an embodiment of an electronic device in which an embodiment of theinvention may be implemented.

DETAILED DESCRIPTION

In this section we shall explain several preferred embodiments of thisinvention with reference to the appended drawings. Whenever the shapes,relative positions and other aspects of the parts described in theembodiments are not clearly defined, the scope of the invention is notlimited only to the parts shown, which are meant merely for the purposeof illustration. Also, while numerous details are set forth, it isunderstood that some embodiments of the invention may be practicedwithout these details. In other instances, well-known structures andtechniques have not been shown in detail so as not to obscure theunderstanding of this description.

FIG. 1A illustrates a cross-sectional side view of one embodiment of aMEMS device. MEMS device 100 may, in some embodiments, be any type ofMEMS sensor that can benefit from being able to tilt one or more platesor layers within the sensor as described herein. For example, MEMSdevice 100 may be an optical microphone, an inertial sensor, anaccelerometer, a gyrometer or the like. Representatively, in oneembodiment, device 100 includes a top plate 102, a middle plate 104 anda bottom plate 106. Each of top plate 102, middle plate 104 and bottomplate 106 may be parallel to one another in one state, and extendhorizontally from vertically extending support members 108A or 108B ofsubstrate 110 (i.e. top plate 102, middle plate 104 and bottom plate 106are perpendicular to support members 108A-108B). In one embodiment,vertically extending support members 108A and 108B may be sidewalls of acavity 140 which is pre-formed within substrate 110 before each of topplate 102, middle plate 104 and bottom plate 106 are formed using MEMSprocessing techniques (e.g. deposition processes, patterning,lithography, etching, etc).

In one embodiment, top plate 102 is attached at one end 128 tovertically extending support member 108B by a spring 112, or othersimilar structure that allows for movement of top plate 102 with respectto support member 108B. The other end of top plate 102 is a free end 130that is not directly connected to another structure (e.g., the free end130 is not connected to support member 108A). Similarly, middle plate104 is attached at one end 132 to support member 108B by a spring 114and the other end is a free end 134 that is not directly connected toanother structure. Top plate 102 and middle plate 104 may have a similarlength, which is slightly less than the distance between support member108A and 108B. Middle plate 104 is spaced a distance below top plate 102by spacers 116A and 116B. Spacers 116A and 116B may be formed on abottom side of top plate 102, or a top side of middle plate 104, suchthat they space one plate from the other.

Bottom plate 106 extends from vertically extending support member 108A,in a direction toward support member 108B. Middle plate 104 is spaced adistance from bottom plate 106 by spacer 136. Unlike top plate 102 andmiddle plate 104, bottom plate 106 is a stationary structure which isfixedly attached to support member 108B. In some embodiments, bottomplate 106 has a length which is shorter than a length of top plate 102and middle plate 104. For example, bottom plate 106 extends a distancefrom support member 108A such that it is beneath the free ends 130, 134of top plate 102 and middle plate 104, but less than the entire lengthof top plate 102 and bottom plate 104. In other embodiments, bottomplate 106 may extend from support member 108B, in a direction of supportmember 108A, and in some cases, extend all the way to support member108A such that both ends are fixed to respective support members108A-108B. In each embodiment, it is important that bottom plate 106have a length sufficient provide a fixed support surface below middleplate 104 for tilting of middle plate 104.

Device 100 may further include a circuit 124 (e.g. an applicationspecific integrated circuit (ASIC)) electrically connected to top plate102, middle plate 104 and bottom plate 106 by wiring 118, 120 and 122,respectively. Wiring 118, 120 and 122 may run through substrate 110 andsupport members 108A-108B to the respective plates 102, 104 and 106. Inone embodiment, circuit 124 may be configured to receive power from anexternal source and apply a voltage to one or more of top plate 102,middle plate 104 and bottom plate 106. The application of a voltage toone or more of top plate 102, middle plate 104 and bottom plate 106 canbe used to tilt the plates from the resting, and in this examplehorizontal, position shown in FIG. 1A.

FIG. 1B illustrates the MEMS device of FIG. 1A in a tiltedconfiguration. Representatively, the application of the voltage to oneor more of top plate 102, middle plate 104 and bottom plate 106 throughcircuit 124 creates electrostatic forces between each plate which causethe plates to be drawn toward one another. In other words, top plate102, middle plate 104 and bottom plate 106 act as electrodes which areelectrically isolated from one another by spacers 116A, 116B, 136 suchthat capacitors are formed between each of the plates. Therefore, whenthe appropriate voltage is applied to each of top plate 102, middleplate 104 and bottom plate 106, the resulting electrostatic forces causethem to become clamped together. In one embodiment, the voltage can beapplied as a direct current (DC) voltage. Alternatively, the voltage canbe an alternating current (AC) voltage. Since end 128 of top plate 102and end 132 of middle plate 104 are connected to support member 108B bysprings 112 and 114, respectively, the greatest degree of movementoccurs at free ends 130, 134. Still further, since bottom plate 106 isstationary, free end 130 of top plate 102 and free end 134 of middleplate 104 move toward bottom plate 106 resulting in top plate 102 andmiddle plate 104 having a tilted configuration in which ends 128, 132are higher than free ends 130, 134.

Representatively, when the appropriate voltage is applied to each of topplate 102, middle plate 104 and bottom plate 106, the free end 134 ofthe middle plate 104 moves toward the bottom plate 106 (which isstationary) to tilt the middle plate 104 and set the tilt angle 126. Inaddition, the free end 130 of top plate 102 moves toward middle plate104 to tilt the top plate 102. In this aspect, top plate 102 and middleplate 104 can be accurately tilted to an optimal and fine tuned tiltangle 126, which provides a desired device performance (e.g. directslight reflected off the plates toward a detector). For example, in oneembodiment, the angle 126 may be an acute angle, for example, less than4 degrees, for example, 3 degrees or less. It is further to beunderstood that spacers 116A, 116B and 136 are dimensioned to maintainan even space or gap between top plate 102, middle plate 104 and bottomplate 106 so that stiction between the plates is avoided and acontrolled minimal stress region of operation between top plate 102 andmiddle plate 104 can be maintained. In this aspect, a device which isformed using MEMS processing techniques is provided which includescomponents (e.g. plates) that can be tilted from an otherwise horizontalorientation typically found in MEMS devices.

FIG. 2A illustrates a cross-sectional side view of another embodiment ofa MEMS device. In this embodiment, the MEMS device is a MEMS opticalmicrophone 200. In this aspect, since the MEMS device is an opticalmicrophone, each of the previously discussed plates 102, 104 and 106,although operable in the manner previously discussed, are manufacturedusing MEMS processing techniques to carry out the functions of anoptical microphone. Representatively, microphone 200 may include a topplate such as compliant membrane 202, a middle plate such as back plate204, a bottom plate such as base plate 206, an emitter 260 and adetector 262. Each of compliant membrane 202, back plate 204, base plate206, and in some cases emitter 260 and detector 262, may be built onsubstrate 210 using MEMS processing techniques. Substrate 210 may bemounted within a frame or enclosure 240. Enclosure 240 may include anacoustic port 242 through which sound (S) (also referred to as acousticwaves) can travel into microphone 200. Although acoustic port 242 isillustrated along a top side of enclosure 240, it could also be along abottom side or side wall of enclosure 240 (while still allowing theacoustic waves to reach the compliant membrane 202) and therefore is notlimited to the illustrated location.

Compliant membrane 202 may be configured to vibrate in response to sound(S) (acoustic waves) entering enclosure 240 through acoustic port 242.In this aspect, compliant membrane 202 may also be referred to as adiaphragm. Compliant membrane 202 may be made of any material and haveany dimensions suitable to provide a semi-rigid or compliant membranethat vibrates in response to sound waves, for example, polysilicon. Inaddition, compliant membrane 202 may be made of, or have a materialintegrated therein, that allows for compliant membrane 202 to functionas an electrode. In some embodiments, a center portion 270 of compliantmembrane 202 may be considered the portion that vibrates while the outerportions primarily serve as a rigid frame to support center portion 270as will be discussed in more detail in reference to FIG. 3. In thisaspect, the center portion 270 may be more compliant than the outerportions.

In addition, a reflective surface 272 may be formed on a side of centerportion 270 facing emitter 260 and detector 262 such, that a vibrationof center portion 270 can be detected by reflecting a light emitted byemitter 260 toward detector 262. In some embodiments, the center portion270 is made of a reflective material (e.g. metallic foil) while in otherembodiments, the reflective surface 272 is formed by application of acoating (e.g. metal coating such as gold) to center portion 270.Although reflective surface 272 is shown positioned only within centerportion 270, it is contemplated that the reflective surface may extendbeyond center portion, for example, to the ends 230, 228 of compliantmembrane 202. Compliant membrane 202, including center portion 270 andreflective surface 272, may be built upon substrate 210 using MEMSprocessing techniques (e.g. deposition processes, patterning,lithography, etching, etc.).

Back plate 204 may be a substantially rigid plate positioned betweencompliant membrane 202 and emitter 260 and detector 262. For example,back plate 204 may be made of a thick and stiff silicon plate. Inaddition, back plate 204 may be made of, or have a material integratedtherein, that allows for back plate 204 to function as an electrode thatcan be tilted as described herein. Back plate 204 may include a grating280 aligned with emitter 260 and detector 262 such that light directedtoward reflective surface 272 and light reflected from reflectivesurface 272 passes through grating 280. Grating 280 is dimensioned toform an interference pattern which can be detected by detector 262 andused as an indicator of a movement of compliant membrane 202. Since thepattern represents a displacement of the compliant membrane 202, it canbe used to provide an indication of sound using a diffraction basedoptical interferometer method or any other optical interferometricmethod. Representatively, in some embodiments, grating 280 may alsoinclude a reflective coating 282 to facilitate formation of theinterference pattern. Back plate 204, including grating 280, may bebuilt upon substrate 210 using MEMS processing techniques (e.g.deposition processes, patterning, lithography, etching, etc.).

Base plate 206 may be a substantially rigid plate positioned betweenback plate 204 and emitter 260 and detector 262. Base plate 206 may be afixed structure that is built upon substrate 210 using MEMS processingtechniques (e.g. deposition processes, patterning, lithography, etching,etc.). In this aspect, base plate may be made of a similar material, ordifferent material, as back plate 204, for example, a silicon material.

In one embodiment, in their untilted state, each of compliant membrane202, back plate 204 and base plate 206 are parallel to one another andextend in a direction perpendicular to vertically extending supportmembers 208A or 208B (e.g. horizontally). Vertically extending supportmembers 208A and 208B may be members which extend in a directionperpendicular to a horizontal base portion 250 of substrate 210.Vertically extending support members 208A and 208B may be pre-formedportions of substrate 210 (i.e. sidewalls of a cavity 290 formed withinsubstrate 210) or formed on top of substrate 210 using MEMS techniques.

Compliant membrane 202 is attached at one end 228 to verticallyextending support member 208B by a spring 212, or other similarstructure that allows for a pivot or hinge type movement of compliantmembrane 202 with respect to support member 208B. Representatively,spring 212 may be a tension/extension spring, a flat spring, acorrugated structure, or an arm member which has some degree ofelasticity to allow for compliant membrane 202 to be tilted withoutinterfering with a vibration of compliant membrane 202 in response tosound waves. The other end of compliant membrane 202 is a free end 230that is not directly connected to another structure (e.g., the free endis not connected to support member 208A). In this aspect, free end 230is free to move up or down while a vertical position of end 228 alongsupport member 208B remains substantially the same. Compliant membrane202 may have a length which is slightly less than a distance betweensupport member 208A and 208B such that it can be tilted between members208A and 208B.

Back plate 204 is attached at one end 232 to support member 208B. Backplate 204 may be attached to support member 208B at a position below end228 of compliant membrane 202 such that back plate 204 is betweencompliant membrane 202 and base plate 206. End 232 of back plate 204 maybe attached to support member 208B by a spring 214. Spring 214 may besimilar to spring 212. The other end of back plate 204 is a free end 234that is not directly connected to another structure (e.g. not directlyconnected to support member 208B). In this aspect, free end 234 is freeto move up or down while a vertical position of end 232 along supportmember 208B remains substantially the same such that back plate 204 canbe tilted similar to compliant membrane 202. Back plate 204 may have alength which is slightly less than a distance between support member208A and 208B such that it can be tilted between members 208A and 208B.

Compliant membrane 202 is spaced a distance from back plate 204 byspacers 216A and 216B. Spacers 216A and 216B may be attached to a bottomsurface of compliant membrane 202 or a top surface of back plate 204.Spacers 216A and 216B may be of a dimension and material which allowsthem to both mechanically and electrically isolate compliant membrane202 from back plate 204. Representatively, spacers 216A and 216B may bemade of an insulating material, for example, porcelain (ceramic), glass,mica, plastics, and the oxides of various metals.

Base plate 206 extends from vertically extending support member 208A, ina direction toward support member 208B. Base plate 206 may be at aposition along support member 208A which is below back plate 204 suchthat base plate 206 is between back plate 204 and substrate 210. Baseplate 206 is positioned a distance from back plate 204 by spacer 236.Spacer 236 may be attached to one of a bottom side of back plate 204 ora top side of base plate 206 and be of a dimension and material suchthat it both mechanically and electrically isolates back plate 204 frombase plate 206. Representatively, spacer 236 may be made of aninsulating material (e.g., porcelain (ceramic), glass, mica, plastics,and the oxides of various metals).

Unlike compliant membrane 202 and back plate 204, base plate 206 is astationary structure which is fixedly attached to support member 208B.In some embodiments, base plate 206 has a length which is shorter than alength of compliant membrane 202 and back plate 204. For example, baseplate 206 extends a distance from support member 208A such that it isbeneath the free ends 230, 234 of compliant membrane 202 and back plate204, but not beneath the entire length of compliant membrane 202 andbase plate 204. In other embodiments, base plate 206 extends fromsupport member 208A to support member 208B such that it extends theentire distance between support members 208A-208B and, in some cases, isfixed at both ends to the respective support member 208A-208B.

Device 200 may further include a circuit 224 (e.g. an applicationspecific integrated circuit (ASIC)) attached to compliant membrane 202,back plate 204 and base plate 206 by wiring 218, 220 and 222,respectively. Wiring 218, 220 and 222 may run through substrate 210 andsupport members 208A-208B to the respective one of membrane 202, backplate 204 and base plate 206. In one embodiment, the circuit 224 may beconfigured to receive power from an external source and apply a voltageto one or more of compliant membrane 202, back plate 204 and base plate206. The application of a voltage to one or more of compliant membrane202, back plate 204 and base plate 206 can be used to tilt the platesfrom the otherwise horizontal position shown in FIG. 2A. When thevoltage is removed, compliant membrane 202, back plate 204 and baseplate 206 may return to the resting position (i.e. horizontal position).

In addition, circuit 224 may be connected to emitter 260 and detector262 by wiring 284, 286, respectively. Wiring 284, 286 may run throughsubstrate 210 and support members 208A-208B to emitter 260 and/ordetector 262. In this aspect, circuit 224 may receive power from anexternal source and provide power to emitter 260 and/or detector 262. Insome embodiments, emitter 260 may be a light source such as a VCSEL,that is electrically connected to substrate 210. Emitter 260 may beconfigured to emit a laser light (or beam) in the direction of grating280 and reflector 282, for detection by detector 262. Detector 262 may,in some embodiments, be a photo detector configured to detect areflected light (or beam) generated by emitter 260. The emitter 260(e.g. VCSEL) and detector 262 (e.g. photo detector) can be off the shelfcommercially available parts or custom built for a specificimplementation.

Each of compliant membrane 202, back plate 204 and base plate 206 areparallel to one another and substantially planar structures which aremanufactured in a horizontal configuration. Emitter 260 is directlybelow compliant membrane 202 and back plate 204 such that light emittedfrom emitter 260 is directed “straight on” toward compliant membrane 202and back plate 204. In this configuration, however, the light willreflect off of reflective surface 272 of compliant membrane 202 back toemitter 260, not detector 262, as illustrated by dashed arrow 288. Inthis aspect, to properly align, the reflected light and direct the lightto detector 262, compliant membrane 202 and back plate 204 are tilted asillustrated in FIG. 2B. It is noted that the light is directed bytilting only compliant membrane 202 and back plate 204, not emitter 260,detector 262 and/or substrate 210 thus providing a microphone which canbe mass produced using MEMS processing techniques and without addingtolerances associated with, for example, positioning emitter 260 and/ordetector 262 at an angle.

As can be seen from FIG. 2B, tilting of compliant membrane 202 and baseplate 204, causes reflected light 288 to be directed toward detector262. Representatively, during operation, a voltage is applied tocompliant membrane 202, back plate 204 and base plate 206 throughcircuit 224. The voltage creates electrostatic forces between each platecausing them to be drawn toward one another. In other words, compliantmembrane 202, back plate 204 and base plate 206 act as electrodes whichare electrically isolated from one another by spacers 216A, 216B and 236such that capacitors are formed between each of the plates. Therefore,when the voltage is applied to each of compliant membrane 202, backplate 204 and base plate 206, the electrostatic forces cause them tobecome clamped together. In one embodiment, the voltage can be appliedas a direct current (DC). Alternatively, the voltage can be analternating current (AC). Since one end 228, 232 of compliant membrane202 and back plate 204, respectively, are maintained at a verticalposition along support member 208B by springs 212 and 214, respectively,only their free ends 230, 234 move toward one another. Still further,since base plate 206 is stationary, free ends 230, 234 of compliantmembrane 202 and back plate 204, respectively, move toward base plate206 resulting in compliant membrane 202 and back plate 204 having atilted configuration.

Representatively, when the voltage is applied to one or more ofcompliant membrane 202, back plate 204 and base plate 206, the free end234 of the back plate 204 moves toward the base plate 206 (which isstationary) to tilt the back plate 204 and set the tilt angle 226. Insome embodiments, spacer 236 rests on base plate 206 to set a fixed tiltangle 226. The free end 230 of compliant membrane 202, in turn, movestoward back plate 204 to tilt the compliant membrane 202. In someembodiments, spacers 216A-216B rest on back plate 204 such thatcompliant membrane 202 is at the same angle as back plate 204. In thisaspect, compliant membrane 202 and back plate 204 can be tilted to anoptimal and fine tuned tilt angle 226, which provides a desired deviceperformance (e.g. directs reflected light toward detector 262). Forexample, in one embodiment, the angle 226 may be an acute angle, forexample, less than 4 degrees, for example, 3 degrees or less. It isfurther contemplated that in some embodiments, different, orintermediate, tilt angles may be achieved depending, for example, upon avoltage applied to the circuitry 224. For example, in some embodiments,the application of a smaller voltage causes back plate 204 to tilttoward, but not touch, base plate 206, thus resulting in a smaller tiltangle being set by back plate 204. The application of a larger voltagewill, in turn, draw back plate 204 closer to base plate 206, thusresulting in a larger tilt angle being set by back plate 204.Application of a similar voltage to compliant membrane 202 will thencause compliant membrane 202 to tilt to the same angle as back plate204. It is further to be understood that spacers 216A, 216B and 234 aredimensioned to maintain an even, space or gap between compliant membrane202, back plate 204 and base plate 206 so that stiction between theplates is avoided and a controlled minimal stress region of operationbetween compliant membrane 202 and back plate 204 can be maintained.

Detector 262 then detects the reflected light 288 and provides anindication of sound. In particular, compliant membrane 202 vibrates inresponse to sound (S). The vibration of compliant membrane 202 modulatesan intensity of light 288 reflected off of the reflective surface 272 ofcompliant membrane 202. In addition, movement of compliant membrane 202with respect to grating 280 (which is rigid) causes an interferencepattern formed by grating 280 to change in size. This modulation inintensity (i.e. change in size of the interference pattern) is detectedby detector 262 and used as an indication of the movement of membrane202 and in turn, provides an indication of sound. It is further to beunderstood that in order to determine sound from the interferencepattern, a distance between compliant membrane 202 and back plate 204 isset such that it is an integer multiple of ¼λ of the light 288.

FIG. 3 illustrates a top view of the compliant membrane of the opticalmicrophone of FIG. 2. From this view, it can be seen that compliantmembrane 202 may have a center portion 270 suspended within an outerframe 302 by spokes 304A, 304B, 304C and 304D. Center portion 270 may bea compliant membrane configured to vibrate in response to acoustic orsound waves while spokes 304A-304D and frame 302 are substantiallyrigid. In this aspect, center portion 270 may be considered the primarysound pick up surface area of compliant membrane 202 which is used todetect sound while the outer portions (spokes 304A-304D and/or frame302) are used to suspend the center portion 270 in the desired location.In some embodiments, center portion 270, spokes 304A-304D and frame 302are made from a single material layer using MEMS processing techniques.In one embodiment, center portion 270 is thinner (in the z-heightdirection) than spokes 304A-304D and frame 302 such that center portion270 is considered compliant (can vibrate in response to acoustic waves)while outer portions (spokes 304A 304D and frame 302) are substantiallyrigid and unresponsive to acoustic waves.

In one embodiment, center portion 270 is a substantially square shapedmembrane having dimensions sufficient to achieve a desired acousticvibration. In other embodiments, center portion 270 may have any type ofquadrilateral shape, or other shapes, for example, a circle, ellipse,oval or the like. In the case of a square shaped center portion 270,each of spokes 304A-304D may extend from a respective side of centerportion 270 to frame 302. Membrane frame 302, may in turn, be a squareshaped structure. Each of the sides of frame 302 may run parallel to arespective side of center portion 270. In other embodiments, spokes304A-304D and frame 302 may be oriented in any manner with respect tocenter portion 270 that is sufficient to suspend center portion 270above back plate 204, base plate 206 and emitter 260/detector 262 aspreviously discussed.

Spring 212 runs along one side of frame 302 so that it can be used toattach frame 302 to support member 208B as discussed in reference toFIG. 2A. Spring 212 can run along an entire length of the side of frame302, or less than the entire length. Spring 212 can be made from thesame material layer used to form compliant membrane 202 such that it isintegrally formed with compliant membrane 202 using MEMS processingtechniques. For example, frame 302 may be wider on the side where it isdesirable to have spring 212. Corrugations 306 may then be formed in theextra width portion of frame 302 to form an elastic structure thatfunctions as a spring. In other embodiments, spring 212 may have anystructure sufficient to suspend complaint membrane 202 from supportmember 208B and allow compliant membrane 202 to tilt as previouslydiscussed in reference to FIG. 2B.

FIG. 4 illustrates a bottom view of the compliant membrane of FIG. 3.From this view, it can be seen that the bottom surface of center portion270 includes a reflective surface 272. In some embodiments, reflectivesurface 272 is confined to only the area of center portion 270 sincethis is the sound pick up area of compliant membrane 202, and thereforethe portion used to provide an indication of sound. In otherembodiments, reflective surface 272 is formed along the entire bottomside of compliant membrane 202 (e.g., also along spokes 304A-304D and/orframe 302). For example, in embodiments where reflective surface 272 isa coating (e.g. a gold coating), it may be applied along the entirebottom side of compliant membrane 202.

Spacers 216A, 216B, 216C and 216D are also shown positioned along thebottom side of compliant membrane 202. Although four spacers 216A-216Dare shown positioned along each of spokes 304A-304D, respectively, it iscontemplated that any number of spacers may be provided and they may bepositioned along any portion of the bottom side of compliant membrane202 sufficient to space compliant membrane 202 a distance from backplate 204. Spacers 216A-216D may further have any size and shapesuitable for spacing compliant membrane 202 a distance from back plate204. Representatively, spacers 216A-216D may be cone, pyramid, cube, orhemispherically shaped structures. Spacers 216A-216D should be of anymaterial sufficient to both mechanically and electrically isolatecompliant membrane 202 a distance from back plate 204. For example,spacers 216A-216D may be made of an insulating material as previouslydiscussed. In one embodiment, spacers 216A-216D may be formed from adifferent material layer than compliant membrane 202 using MEMSprocessing techniques.

FIG. 5 illustrates a top view of a back plate of the optical microphoneof FIG. 2A. Back plate 204 may be a substantially rigid plate havinggrating 280, which can be formed therein by MEMS processing techniques.Back plate 204 may have a similar size and shape as compliant membrane202, for example a square shape. Alternatively, back plate 204 may haveany type of quadrilateral shape, or other shapes, for example, a circle,ellipse, oval or the like. Grating 280 may have a periodic structuresufficient to split and diffract light emitted from an emitter (e.g.emitter 260) into different beams for detection by a detector (e.g.detector 262). In some embodiments, the grating 280 causes the formationof an interference pattern which can be used to indicate a movement ofcompliant membrane 202 in response to sound waves, and in turn, as anindicator of sound. Grating 280 may be formed in a portion of back plate204 which is aligned with center portion 270 of compliant membrane 202and emitter 260/detector 262, as described in FIG. 2A. In theillustrated embodiment, grating 280 is formed in a center portion ofback plate 204 which, when microphone 200 is assembled, causes grating280 to be positioned between center portion 270 of compliant membrane202 and emitter 260/detector 262.

Spring 214 runs along one side of back plate 204 so that it can be usedto attach back plate 204 to support member 208B as discussed inreference to FIG. 2A. Spring 214 can run along an entire length of theside of back plate 204 or less than the entire length. Spring 214 can bemade from the same material layer used to form back plate 204 such thatit is integrally formed with back plate 204 using MEMS processingtechniques. For example, back plate 204 may be wider on the side whereit is desirable to have spring 214. Corrugations 406 may then be formedin the extra width portion of back plate 204 to form an elasticstructure that functions as a spring. In other embodiments, spring 214may have any structure sufficient to suspend back plate 204 from supportmember 208B and allow back plate 204 to tilt as previously discussed inreference to FIG. 2B.

FIG. 6 illustrates a bottom view of the back plate of FIG. 5. From thisview, it can be seen that back plate 204 includes a reflective layer 282along its bottom side. Reflective layer 282 may also, in someembodiments, be formed along the top side of back plate 204. Forexample, reflective layer 282 may be formed along all surfaces ofgrating 280 to form a grating which is reflective from all angles.Reflective layer 282 may be a material layer, which is formed on backplate 204, or a coating (e.g. a gold coating) which is applied to one ormore surfaces of back plate 204. Alternatively, back plate 204 may bemade of a reflective material such that any outer surfaces of back plate204 are reflective.

FIG. 7A illustrates one embodiment of a processing step for fabricatingthe optical microphone of FIG. 2A. FIG. 7A illustrates substrate 702having a cavity 701 formed therein. Substrate 702 may be a siliconsubstrate, for example, a silicon on insulator (SOI) wafer. Cavity 701may be defined by vertically extending support member 704A andvertically extending support member 704B and a base portion 703 ofsubstrate 702. In one embodiment, cavity 701 is formed within substrate702 using a MEMS etching process for example, reactive ion etching(RIE). Alternatively, cavity 701 may be formed on top of substrate 702by stacking additional material layers and then patterning the layers toform cavity 701. MEMS microphone 200 may be formed within cavity 701.

Representatively, in one embodiment, a sacrificial layer 706 may beformed on top of the base portion 703 of substrate 702. Sacrificiallayer 706 may be formed by any MEMS processing technique suitable forforming a sacrificial layer. For example, sacrificial layer 706 may beformed by blanket depositing a sacrificial material over substrate 702using a chemical vapor deposition (CVD) process and then planarizing thelayer to provide a desired layer thickness. Sacrificial layer 706 may bemade of any material that can be selectively removed or patterned usingMEMS processing steps. Representatively, sacrificial layer 706 may bemade of silicon dioxide or a silicate glass.

Base plate layer 708 may be formed over sacrificial layer 706. Baseplate layer 708 may be formed by any MEMS processing technique suitablefor forming a base plate layer, for example, blanket depositing a baseplate layer material using CVD. Base plate layer 708 may be made of anymaterial suitable for forming, for example base plate 206 previouslydiscussed in reference to FIG. 2A. Representatively, base plate layer708 may be made of a silicon material.

FIG. 7B illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7B shows base platelayer 708 after a processing step in which portions of base plate layer708 are removed to form a structure suitable for use as a base platewithin microphone 200. For example, base plate layer 708 may bepatterned using different etching steps (e.g. reactive ion etching) tohave the shape and dimensions of base plate 206 described in referenceto FIG. 2A. Since base plate layer 708 is to be used as the basestructure which supports the tilt of other plates (or membranes) (e.g.membrane 202 and back plate 204 discussed in reference to FIG. 2A),sacrificial layer 706 should have a thickness equal to the desireddistance or gap between the base plate of the microphone and thesubstrate (e.g. substrate 210) so that when sacrificial layer 706 isremoved a space or gap of the desired size remains between thestructures.

FIG. 7C illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7C illustrates thestep of forming a sacrificial layer 710 over base plate layer 708.Sacrificial layer 710 may be formed using any MEMS processing stepsuitable for forming a sacrificial layer over another layer. Forexample, sacrificial layer 710 may be formed by blanket depositing asacrificial layer material over base plate layer 708 and sacrificiallayer 706 using CVD. Sacrificial layer 710 may be substantially similarto sacrificial layer 706. Sacrificial layer 708 may be of any materialthat can be selectively removed during a further processing step (e.g.silicon dioxide or silicate glass).

FIG. 7D illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7D illustrates thestep of forming a back plate layer 712 over sacrificial layer 710. Backplate layer 712 may be formed by any MEMS processing step suitable forforming a back plate layer over sacrificial layer 710. For example, backplate layer 712 may be formed by blanket depositing a back plate layermaterial over sacrificial layer 710 using CVD. A suitable back platelayer material may be, for example, a silicon material capable offorming a substantially rigid layer that can function as an electrodeduring operation of the microphone.

FIG. 7E illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7E shows back platelayer 712 after a processing step in which portions of back plate layer712 are removed to form a structure suitable for use as a back platewithin microphone 200. For example, back plate layer 712 is processedusing MEMS processing techniques to have the shape and dimensions ofback plate 204 described in reference to FIG. 2A. Representatively, anRIE processing technique may be used to pattern back plate layer 712such that it is separated from support member 704A and includes grating714 and spring 716. Grating 714 and spring 716 may be substantiallysimilar to grating 280 and spring 214 previously discussed in referenceto FIG. 2A.

It should further be understood that since back plate layer 712 (e.g.back plate 204) is designed to be tilted onto base plate layer 708 (e.g.base plate 206) in the final product, a distance between back platelayer 712 and base plate layer 708, as well as a length of back platelayer 712, are selected to achieve the desired tilt angle. In otherwords, the tilt angle is controlled by the thickness of sacrificiallayer 710 between base plate layer 708 and back plate layer 712. In thisaspect, a thickness of sacrificial layer 710, is selected to achieve thedesired tilt angle between the layers, for example, an acute tilt anglesuch as an angle of 4 degrees or less, for example, 3 degrees.

FIG. 7F illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7F illustrates thestep of forming a sacrificial layer 718 over back plate layer 712.Sacrificial layer 718 may be formed using any MEMS processing stepsuitable for forming a sacrificial layer over another layer. Forexample, sacrificial layer 718 may be formed by blanket depositing asacrificial layer over back plate layer 712 and sacrificial layer 710using CVD. Sacrificial layer 718 may be substantially similar tosacrificial layers 706 and 710. Sacrificial layer 718 may be of anymaterial that can be selectively removed during a further processingstep (e.g. silicon dioxide or silicate glass).

FIG. 7G illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7G illustrates thestep of forming a compliant membrane layer 720 over sacrificial layer718. Compliant membrane layer 720 may be formed by any MEMS processingstep suitable for forming a compliant membrane layer 720 oversacrificial layer 718. For example, compliant membrane layer 720 may beformed by blanket depositing a compliant membrane material oversacrificial layer 718 using CVD. A compliant membrane material mayinclude, but is not limited to, a material capable of forming a membranethat can function as a microphone diaphragm and an electrode during atilting operation of the microphone, for example, polysilicon or ametallic material.

FIG. 7H illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7H shows compliantmembrane layer 720 after a processing step in which portions ofcompliant membrane layer 720 are patterned to form a structure suitablefor use as a compliant membrane (e.g. a diaphragm) within microphone200. For example, compliant membrane layer 720 is patterned using an RIEtechnique to have the shape and dimensions of compliant membrane 202described in reference to FIG. 2A. Representatively, RIE may be used toseparate compliant membrane layer 720 from support member 704A as wellas to form a more compliant center portion 724 (a portion with reducedthickness), a more rigid frame 760 (a portion thicker than centerportion 724) and spring 722. Center portion 724 and spring 722 may besubstantially similar to center portion 270 and spring 212 previouslydiscussed in reference to FIG. 2A and frame 760 may be substantiallysimilar to frame 302 discussed in reference to FIG. 3.

FIG. 7I illustrates one embodiment of another processing step forfabricating the optical microphone of FIG. 2A. FIG. 7I shows formationof an opening 730 within substrate 702. Opening 730 can be formed by anystandard MEMS processing technique, for example, RIE or a deep reactiveion etching (DRIE) step. Opening 730 facilitates removal of sacrificiallayers 706, 710 and 718.

Representatively, FIG. 7J illustrates a processing step in whichsacrificial layers 706, 710 and 718 have been removed, for example, by awet or dry etch processing technique. For example, layers 706, 710 and718 may be removed using a wet etching step with a selective wet etchantincluding hydrofluoric acid (HF). The wet etchant (HF) etches awaysacrificial layers 706, 710 and 718 without etching, or otherwisedamaging, the various layers needed to form the microphone, for example,base plate layer 708, back plate layer 712 and compliant membrane layer720. In some embodiments, portions of sacrificial layers 718 and 710 maybe patterned and not completely removed such that spacers 750, 752A and752B, which, for example, correspond to spacers 236, 216A and 216Bremain between the layers.

FIG. 7J further illustrates the step of applying a reflective surface736 to center portion 718 and a reflective surface 734 to grating 714.Representatively, in one embodiment, reflective surface 736 andreflective surface 734 are formed by introducing a reflective material732 (e.g., gold coating) through opening 730 within substrate in amanner that allows material 732 to coat center portion 718 and grating714.

Once each of the layers necessary for operation of microphone 700 areformed, an emitter (e.g. emitter 260) and detector (e.g. detector 262)can be positioned within opening 730 such that they are aligned withgrating 714 and reflective surface 736. In one embodiment, emitter anddetector may be formed monolithically on another substrate usingstandard MEMS processing techniques, and then positioned within, oraligned with, opening 730. Microphone 700 may then be mounted within anenclosure (e.g. enclosure 240) which can in turn be mounted within thedesired electronic device. Alternatively, the emitter and detector maybe mounted within an enclosure for the microphone and positioned withinopening 730. In addition, any circuitry (e.g. wires) connected to thevarious microphone components, for example, base layer 708, back platelayer 712, compliant membrane layer 720, the emitter or the detector maybe pre-formed within substrate 702 and support members 704A-704B suchthat when the components are formed, the circuitry is connected to thecomponents.

FIG. 8 illustrates one embodiment of a simplified schematic view of oneembodiment of an electronic device in which a MEMS optical microphone,or other MEMS device described herein, may be implemented. As seen inFIG. 8, the MEMS device may be integrated within a consumer electronicdevice 802 such as a smart phone with which a user can conduct a callwith a far-end user of a communications device 804 over a wirelesscommunications network; in another example, the MEMS device may beintegrated within the housing of a tablet computer. These are just twoexamples of where the MEMS device described herein may be used, it iscontemplated, however, that the MEMS device may be used with any type ofelectronic device in which a MEMS device, for example, an optical MEMSmicrophone, is desired, for example, a tablet computer, a desk topcomputing device or other display device.

FIG. 9 illustrates a block diagram of some of the constituent componentsof an embodiment of an electronic device in which an embodiment of theinvention may be implemented. Device 900 may be any one of severaldifferent types of consumer electronic devices. For example, the device900 may be any microphone-equipped mobile device, such as a cellularphone, a smart phone, a media player, or a tablet-like portablecomputer.

In this aspect, electronic device 900 includes a processor 912 thatinteracts with camera circuitry 906, motion sensor 904, storage 908,memory 914, display 922, and user input interface 924. Main processor912 may also interact with communications circuitry 902, primary powersource 910, speaker 918, and microphone 920. The various components ofthe electronic device 900 may be digitally interconnected and used ormanaged by a software stack being executed by the processor 912. Many ofthe components shown or described here may be implemented as one or morededicated hardware units and/or a programmed processor (software beingexecuted by a processor, e.g., the processor 912).

The processor 912 controls the overall operation of the device 900 byperforming some or all of the operations of one or more applications oroperating system programs implemented on the device 900, by executinginstructions for it (software code and data) that may be found in thestorage 908. The processor 912 may, for example, drive the display 922and receive user inputs through the user input interface 924 (which maybe integrated with the display 922 as part of a single, touch sensitivedisplay panel). In addition, processor 912 may send an audio signal tospeaker 918 to facilitate operation of speaker 918.

Storage 908 provides a relatively large amount of “permanent” datastorage, using nonvolatile solid state memory (e.g. flash storage)and/or a kinetic nonvolatile storage device (e.g., rotating magneticdisk drive). Storage 908 may include both local storage and storagespace on a remote server. Storage 908 may store data as well as softwarecomponents that control and manage, at a higher level, the differentfunctions of the device 900.

In addition to storage 908, there may be memory 914, also referred to asmain memory or program memory, which provides relatively fast access tostored code and data that is being executed by the processor 912. Memory914 may include solid state random access memory (RAM), e.g., static RAMor dynamic RAM. There may be one or more processors, e.g., processor912, that run or execute various software programs, modules, or sets ofinstructions (e.g., applications) that, while stored permanently in thestorage 908, have been transferred to the memory 914 for execution, toperform the various functions described above.

The device 900 may include communications circuitry 902. Communicationscircuitry 902 may include components used for wired or wirelesscommunications, such as two-way conversations and data transfers. Forexample, communications circuitry 902 may include RF communicationscircuitry that is coupled to an antenna, so that the user of the device900 can place or receive a call through a wireless communicationsnetwork. The RF communications circuitry may include a RF transceiverand a cellular baseband processor to enable the call through a cellularnetwork. For example, communications circuitry 902 may include Wi-Ficommunications circuitry so that the user of the device 900 may place orinitiate a call using voice over Internet Protocol (VOIP) connection,transfer data through a wireless local area network.

The device may include a microphone 920. Microphone 920 may be a MEMSoptical microphone such as that described in reference to FIGS. 2A-2B.In this aspect, microphone 920 may be an acoustic-to-electric transduceror sensor that converts sound in air into an electrical signal. Themicrophone circuitry (e.g. circuit 224) may be electrically connected toprocessor 912 and power source 910 to facilitate the microphoneoperation (e.g. tilting).

The device 900 may include a motion sensor 904, also referred to as aninertial sensor, that may be used to detect movement of the device 900.Motion sensor 904 could, in some embodiments, include MEMS device FIG.1A-FIG. 1B. The motion sensor 904 may include a position, orientation,or movement (POM) sensor, such as an accelerometer, a gyroscope, a lightsensor, an infrared (IR) sensor, a proximity sensor, a capacitiveproximity sensor, an acoustic sensor, a sonic or sonar sensor, a radarsensor, an image sensor, a video sensor, a global positioning (GPS)detector, an RF or acoustic doppler detector, a compass, a magnetometer,or other like sensor. For example, the motion sensor 904 may be a lightsensor that detects movement or absence of movement of the device 900,by detecting the intensity of ambient light or a sudden change in theintensity of ambient light. The motion sensor 904 generates a signalbased on at least one of a position, orientation, and movement of thedevice 900. The signal may include the character of the motion, such asacceleration, velocity, direction, directional change, duration,amplitude, frequency, or any other characterization of movement. Theprocessor 912 receives the sensor signal and controls one or moreoperations of the device 900 based in part on the sensor signal.

The device 900 also includes camera circuitry 906 that implements thedigital camera functionality of the device 900. One or more solid stateimage sensors are built into the device 900, and each may be located ata focal plane of an optical system that includes a respective lens. Anoptical image of a scene within the camera's field of view is formed onthe image sensor, and the sensor responds by capturing the scene in theform of a digital image or picture consisting of pixels that may then bestored in storage 908. The camera circuitry 906 may also be used tocapture video images of a scene.

Device 900 also includes primary power source 910, such as a built inbattery, as a primary power supply.

While certain embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat the invention is not limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those of ordinary skill in the art. For example, the devicesand processing steps disclosed herein may correspond to any type of MEMSsensor that can benefit from being able to tilt one or more plates orlayers within the sensor, for example, an inertial sensor, anaccelerometer, a gyrometer or the like. Still further, in someembodiments, the MEMS sensor includes only two plates, and only one ofthe plates is movable. For example, the MEMS sensor may include a topplate having a sensor surface, a base plate and circuitry to apply avoltage between the two plates. The voltage causes only one of theplates to move with respect to the other plate (e.g. the movable platecan be the top plate with the sensor, which could be a sound pick upmembrane). The description is thus to be regarded as illustrativeinstead of limiting.

What is claimed is:
 1. A method of detecting sound using amicro-electro-mechanical system (MEMS) optical microphone, the methodcomprising: providing the MEMS optical microphone having a compliantmembrane with a reflective portion configured to vibrate in response toan acoustic wave, a back plate having a grating, a base plate, a lightemitter, a light detector and circuitry; applying a voltage, using thecircuitry, to tilt the compliant membrane and the back plate withrespect to the base plate; illuminating the reflective portion of thecompliant membrane with a light emitted from the light emitter; anddetecting, using the light detector, a diffracted pattern of the lightfrom the light emitter after reflection from the reflective portion toprovide an indication of sound.
 2. The method of claim 1 wherein a tiltangle of the compliant membrane and the back plate is 4 degrees or less.3. The method of claim 1 wherein the base plate is stationary and thecompliant membrane and the back plate are movable.
 4. The method ofclaim 1 wherein the voltage produces an electrostatic force between thecompliant membrane, the back plate and the base plate which draws thecompliant membrane and the back plate toward the base plate.
 5. Themethod of claim 1 wherein an angle of the tilt of the compliant membraneand the back plate with respect to the base plate is variable based onthe voltage applied.
 6. The method of claim 1 wherein the tilt of thecompliant membrane and the back plate with respect to the base plate isat an acute angle.
 7. The method of claim 1 wherein the compliantmembrane and the back plate are tilted at an angle sufficient to causethe diffracted pattern of the light to reflect onto the light detector.8. The method of claim 1 wherein prior to applying the voltage, thecompliant membrane and the back plate are in a substantially horizontalposition.
 9. The method of claim 8 further comprising: after applyingthe voltage, removing the voltage to return the compliant membrane andthe back plate to the substantially horizontal position.
 10. The methodof claim 1 wherein at least one of the compliant membrane, the backplate and the base plate comprises an electrode.
 11. The method of claim1 wherein the compliant membrane, the back plate and the base plate arepositioned over the light emitter and the light detector.
 12. The methodof claim 11 wherein the back plate is between the compliant membrane andthe light emitter such that the light emitted by the light emitterpasses through the grating in the back plate prior to contacting thecompliant membrane.
 13. The method of claim 1 further comprising: asubstrate having a based portion and a vertically extending supportportion, and wherein the compliant membrane, the back plate and the baseplate are coupled to the support portion, and the base plate is in afixed position below the compliant membrane and the back plate.
 14. Themethod of claim 13 wherein the compliant membrane and the back plate arecoupled to the support portion by a spring.
 15. The method of claim 1further comprising: at least one spacer positioned between the compliantmembrane and the back plate, and wherein the spacer mechanically andelectrically isolates the compliant membrane from the back plate.